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this indeed appears but a feeble tribute of respect to the services 
which he has rendered to the science of mineralogy. 

Since the crystallization of certain mineral substances, in which 
nothing but earths has been discovered, has appeared problematical 
to many persons, and has led to the supposition of the existence of 
unknown acids in their composition, Mr. Smithson endeavours to 
explain this difficulty, by suggesting that quartz itself may be con- 
sidered as an acid, to which class of bodies it has analogous quali- 
ties : we shall then have a numerous class of silicates, both simple 
and compound ; and zeolite will belong to the latter, and may be 
regarded as a hydrated silicate of alumina. 

Experiments and Observations on the different Modes in which Death 
is produced by certain vegetable Poisons. By B. C. Brodie, Esq. 
F.R.S. Communicated by the Society for promoting the Knowledge 
of Animal Chemistry. Read February 21, 1811. [Phil. Trans. 
1811, jp. 178.] 

The substances selected for these experiments are vegetable poisons 
only ; and they were chosen of the most active kind, that the exact 
nature of their effects might be more readily discerned. The prin- 
cipal object of the experiments is to determine on which of the vital 
organs the influence of each poison is exerted, and through what 
medium the organ becomes affected. The first series of experiments 
relates to the effects of internal application to the tongue and ali- 
mentary canal, and the second to the consequences of application to 
external wounds. 

When proof spirit was given to a rabbit in sufficient quantity to kill 
it, the heart was observed to continue in action after apparent death. 

The same observation was made respecting the heart of a cat, 
killed by injecting the root of aconite into the rectum. 

"When the oil distilled from bitter almonds was employed, although 
no more than a single drop had been given to a cat, she died in five 
minutes. Two drops of the same oil injected into the rectum of an- 
other cat, killed it also in five minutes. And the heart, in each in- 
stance, continued acting after apparent death. 

Distilled oil of tobacco exerted nearly the same energy as the 
distilled oil of bitter almonds, and apparently in the same way, as 
the heart was observed to contract after apparent death. 

From this circumstance, Mr. Brodie inferred that these poisons 
exert their primary influence on the brain, and that death ensues in 
consequence of the suspension of respiration, which is dependent on 
the brain. 

When an infusion of tobacco was made use of instead of the em- 
pyreumatic oil, and injected into the rectum, the effects were different 
from any of the preceding, as the heart continued to contract, and 
was uniformly found in a state of extreme distension. Mr. Brodie 
is, however, of opinion, that the heart was not directly affected, but 
through the medium of the nervous system. For when the same 


Infusion was injected into the rectum of a dog whose head had been 
cut off, and whose respiration was kept up by artificial means, the 
heart continued to act in the same manner as in the experiments 
which Mr. Brodie lately communicated to the Society, without being 
sensibly affected by the infusion. 

The author's trials of the external application of poisons were con- 
fined to the essential oil of bitter almonds, the juice of aconite, and 
the South American poison called Woorara. They all produced the 
same effects as the two former had done when applied internally, for 
the heart was observed to contract, as before, long after other sym- 
ptoms of life had ceased ; so that the circulation could be kept up 
by means of artificial respiration. 

With respect to the medium through which poisons affect the 
brain when they are applied to external wounds, the author's expe- 
riments were confined to the woorara. And he endeavoured to de- 
termine whether the influence was conveyed by the nerves, or whether 
the poison itself entered the circulation, either by the absorbents, or 
through the divided veins. By dividing the nerves of a part, the 
efficacy of the woorara did not appear diminished, neither did tying 
up the thoracic duct in any degree interfere with its action. But 
when a ligature was applied round the leg of a rabbit, so as not to 
include the sciatic nerve, the rabbit was not in the least affected by 
the woorara. 

The author consequently infers that the woorara acts upon the 
brain by passing into its substance through the divided vessels of the 
part to which it is applied. 

Since the circulation of an animal could be kept up by an artificial 
respiration, after the brain had been even completely removed, Mr. 
Brodie conceived it possible that the functions of the brain might be 
found to recover from temporary suspension if the circulation were 
continued for a time by artificial respiration, and that thus the life 
of the animal might be preserved. 

After two experiments, which were not attended with complete 
success, a third was made upon a rabbit, by applying distilled oil of 
almonds to a wound in the side. In five minutes it ceased to breathe, 
and was apparently dead ; but by means of artificial respiration con- 
tinued for sixteen minutes, it was completely restored to life ; and on 
the following day appeared not to have suffered from the experiment. 

On the Causes which influence the Direction of the Growth of Roots. 
By Thomas Andrew Knight, Esq. F.R.S. In a Letter to the Right 
Hon. Sir Joseph Banks, Bart. K.B. P.R.S. Read March 7, 1811, 
[Phil. Trans. 1811,^. 209.] 

In a former paper Mr. Knight showed the influence of gravitation 
on the plumule and radicle of germinating seeds ; in the present he 
considers the fibrous roots, which, with little comparative regard to 
gravity, extend themselves in whatever direction the greatest nutri- 
ment or moisture is to be found, with an appearance of predilection,